1. Field of the Invention
The technology of the present disclosure relates to a distance measurement device, a distance measurement control method, and a distance measurement control program.
2. Description of the Related Art
Known is a distance measurement device that measures distance based on a round-trip time of laser light emitted by an emission unit toward a subject assumed as a distance measurement target by a user. In the distance measurement device, a subject image that is formed and acquired by incidence of reflective light from the subject on an image formation optical system is visually recognized by the user through a finder.
Typically, in the case of measuring distance by the distance measurement device, the distance measurement device is used in a state of being gripped by the user. In this state, in the case of occurrence of a hand shake (shake) that is a phenomenon of vibration of the distance measurement device by transmission of vibration of a hand of the user, an optical axis of the image formation optical system included in the distance measurement device varies along with the hand shake. In addition, in the case of the distance measurement device being mounted in a vehicle, transmission of vibration of the vehicle may vibrate the distance measurement device and vary the optical axis of the image formation optical system. In addition, the optical axis of the image formation optical system may vary due to transmission of vibration to the distance measurement device from an external device that is used as being connected to the distance measurement device. Furthermore, the optical axis of the image formation optical system may vary due to vibration of an internal device (for example, a motor) that is mounted in the distance measurement device. Variation of the optical axis means, for example, inclination of the optical axis with respect to a reference axis (for example, the optical axis before occurrence of the hand shake).
An image shake that is a phenomenon of shifting of the subject image from a reference position (for example, the position of the subject image that is acquired in the state of absence of the hand shake) occurs if the optical axis of the image formation optical system varies. The image shake is visually recognized by the user through, for example, the subject image acquired from the image formation optical system through the finder or a picture imaged and acquired by an imaging element and hinders a work of aiming at the subject of the distance measurement target.
As a method for reducing such an image shake, considered is, for example, a method of applying an image shake reduction mechanism mounted in a commercially available imaging device to the distance measurement device.
Generally, the user visually recognizes the subject image through the finder, aims at the subject of the distance measurement target assuming that the center of the subject image is irradiated with laser light, and provides the distance measurement device with an instruction to initiate distance measurement, thereby causing a laser diode to emit the laser light. However, for example, if the hand shake occurs, not only an image shake but also a phenomenon of variation of the optical axis of the laser light with respect to the subject (laser shake) occurs. Thus, even if the image shake is reduced by the image shake reduction mechanism, what may happen is shifting of an irradiation position of the laser light from the center of the subject image, which is the position intended by the user, in the subject image visually recognized by the user. The “irradiation position” refers to, for example, a position in the subject where the laser light hits.
In JP2009-270856A, disclosed is a distance measurement device including a shake reduction function that reduces the image shake and the laser shake. In the distance measurement device disclosed in JP2009-270856A, an optical path on which the optical axis of the image formation optical system coincides with the optical axis of the laser light exists, and an anti-shake lens disposed on the common optical path performs an anti-shake operation, thereby reducing the image shake and the laser shake.